Musnad Ahmad 1:60

'Affan narrated to us, Yazid bin Zuray' narrated to us, Yunus bin 'Ubayd narrated to us, from Humayd bin Hilal, from 'Abdullah bin Mutarrif bin al-Shikhkhir, that he narrated to them from Abu Barzah al-Aslami, that he said: We were with Abu Bakr al-Siddiq during his administration, and he became angry at a man from the Muslims, and his anger toward him became very intense. When I saw that, I said: "O Caliph of the Messenger of Allah, shall I strike his neck?" When I mentioned the killing, he turned away from that entire topic to something else. When we dispersed, Abu Bakr al-Siddiq sent for me after that and said: "O Abu Barzah, what did you say?" He said: "And I had forgotten what I said." I said: "Remind me of it." He said: "Do you not remember what you said?" He said: "I said: No, by Allah." He said: "Do you see when you saw me angry at the man and you said: 'Shall I strike his neck, O Caliph of the Messenger of Allah?' Do you not remember that? Or would you have done that?" He said: "I said: Yes, by Allah, and now if you command me, I will do it." He said: "Woe to you—or: Alas for you—by Allah, that is not for anyone after Muhammad, may Allah bless him and grant him peace."